Statistics and Probability Commons^™

Bootstrap Confidence Intervals For Medical Costs With Censored Observations, Hongyu Jiang, Xiao-Hua Zhou

UW Biostatistics Working Paper Series

Medical costs data with administratively censored observations often arise in cost-effectiveness studies of treatments for life threatening diseases. Mean of medical costs incurred from the start of a treatment till death or certain timepoint after the implementation of treatment is frequently of interest. In many situations, due to the skewed nature of the cost distribution and non-uniform rate of cost accumulation over time, the currently available normal approximation confidence interval has poor coverage accuracy. In this paper, we proposed a bootstrap confidence interval for the mean of medical costs with censored observations. In simulation studies, we showed that the proposed …

A Bootstrap Confidence Interval Procedure For The Treatment Effect Using Propensity Score Subclassification, Wanzhu Tu, Xiao-Hua Zhou

UW Biostatistics Working Paper Series

In the analysis of observational studies, propensity score subclassification has been shown to be a powerful method for adjusting unbalanced covariates for the purpose of causal inferences. One practical difficulty in carrying out such an analysis is to obtain a correct variance estimate for such inferences, while reducing bias in the estimate of the treatment effect due to an imbalance in the measured covariates. In this paper, we propose a bootstrap procedure for the inferences concerning the average treatment effect; our bootstrap method is based on an extension of Efron’s bias-corrected accelerated (BCa) bootstrap confidence interval to a two-sample problem. …

Estimating The Accuracy Of Polymerase Chain Reaction-Based Tests Using Endpoint Dilution, Jim Hughes, Patricia Totten

UW Biostatistics Working Paper Series

PCR-based tests for various microorganisms or target DNA sequences are generally acknowledged to be highly "sensitive" yet the concept of sensitivity is ill-defined in the literature on these tests. We propose that sensitivity should be expressed as a function of the number of target DNA molecules in the sample (or specificity when the target number is 0). However, estimating this "sensitivity curve" is problematic since it is difficult to construct samples with a fixed number of targets. Nonetheless, using serially diluted replicate aliquots of a known concentration of the target DNA sequence, we show that it is possible to disentangle …

Selecting Differentially Expressed Genes From Microarray Experiments, Margaret S. Pepe, Gary M. Longton, Garnet L. Anderson, Michel Schummer

UW Biostatistics Working Paper Series

High throughput technologies, such as gene expression arrays and protein mass spectrometry, allow one to simultaneously evaluate thousands of potential biomarkers that distinguish different tissue types. Of particular interest here is cancer versus normal organ tissues. We consider statistical methods to rank genes (or proteins) in regards to differential expression between tissues. Various statistical measures are considered and we argue that two measures related to the Receiver Operating Characteristic Curve are particularly suitable for this purpose. We also propose that sampling variability in the gene rankings be quantified and suggest using the “selection probability function”, the probability distribution of rankings …

Semiparametric Receiver Operating Characteristic Analysis To Evaluate Biomarkers For Disease, Tianxi Cai, Margaret S. Pepe

UW Biostatistics Working Paper Series

The receiver operating characteristic (ROC) curve is a popular method for characterizing the accuracy of diagnostic tests when test results are not binary. Various methodologies for estimating and comparing ROC curves have been developed. One approach, due to Pepe, uses a parametric regression model with the baseline function specified up to a finite-dimensional parameter. In this article we extend the regression models by allowing arbitrary nonparametric baseline functions. We also provide asymptotic distribution theory and procedures for making statistical inference. We illustrate our approach with dataset from a prostate cancer biomarker study. Simulation studies suggest that the extra flexibility inherent …

Semi-Parametric Regression For The Area Under The Receiver Operating Characteristic Curve, Lori E. Dodd, Margaret S. Pepe

UW Biostatistics Working Paper Series

Medical advances continue to provide new and potentially better means for detecting disease. Such is true in cancer, for example, where biomarkers are sought for early detection and where improvements in imaging methods may pick up the initial functional and molecular changes associated with cancer development. In other binary classification tasks, computational algorithms such as Neural Networks, Support Vector Machines and Evolutionary Algorithms have been applied to areas as diverse as credit scoring, object recognition, and peptide-binding prediction. Before a classifier becomes an accepted technology, it must undergo rigorous evaluation to determine its ability to discriminate between states. Characterization of …

Partial Auc Estimation And Regression, Lori E. Dodd, Margaret S. Pepe

UW Biostatistics Working Paper Series

Accurate disease diagnosis is critical for health care. New diagnostic and screening tests must be evaluated for their abilities to discriminate disease from non-diseased states. The partial area under the ROC curve (partial AUC) is a measure of diagnostic test accuracy. We present an interpretation of the partial AUC that gives rise to a new non-parametric estimator. This estimator is more robust than existing estimators, which make parametric assumptions. We show that the robustness is gained with only a moderate loss in efficiency. We describe a regression modelling framework for making inference about covariate effects on the partial AUC. Such …

Analysis Of Longitudinal Marginal Structural Models , Jennifer F. Bryan, Zhuo Yu, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

In this article we construct and study estimators of the causal effect of a time-dependent treatment on survival in longitudinal studies. We employ a particular marginal structural model (MSM), and follow a general methodology for constructing estimating functions in censored data models. The inverse probability of treatment weighted (IPTW) estimator is used as an initial estimator and the corresponding treatment-orthogonalized, one-step estimator is consistent and asymptotically linear when the treatment mechanism is consistently estimated. We extend these methods to handle informative censoring. A simulation study demonstrates that the the treatment-orthogonalized, one-step estimator is superior to the IPTW estimator in terms …

An Empirical Study Of Marginal Structural Models For Time-Independent Treatment, Tanya A. Henneman, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

In non-randomized treatment studies a significant problem for statisticians is determining how best to adjust for confounders. Marginal structural models (MSMs) and inverse probability of treatment weighted (IPTW) estimators are useful in analyzing the causal effect of treatment in observational studies. Given an IPTW estimator a doubly robust augmented IPTW (AIPTW) estimator orthogonalizes it resulting in a more e±cient estimator than the IPTW estimator. One purpose of this paper is to make a practical comparison between the IPTW estimator and the doubly robust AIPTW estimator via a series of Monte- Carlo simulations. We also consider the selection of the optimal …

The Analysis Of Placement Values For Evaluating Discriminatory Measures, Margaret S. Pepe, Tianxi Cai

UW Biostatistics Working Paper Series

The idea of using measurements such as biomarkers, clinical data, or molecular biology assays for classification and prediction is popular in modern medicine. The scientific evaluation of such measures includes assessing the accuracy with which they predict the outcome of interest. Receiver operating characteristic curves are commonly used for evaluating the accuracy of diagnostic tests. They can be applied more broadly, indeed to any problem involving classification to two states or populations (D = 0 or D = 1). We show that the ROC curve can be interpreted as a cumulative distribution function for the discriminatory measure Y in the …

Case-Control Current Status Data, Nicholas P. Jewell, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

Current status observation on survival times has recently been widely studied. An extreme form of interval censoring, this data structure refers to situations where the only available information on a survival random variable, T, is whether or not T exceeds a random independent monitoring time C, a binary random variable, Y. To date, nonparametric analyses of current status data have assumed the availability of i.i.d. random samples of the random variable (Y, C), or a similar random sample at each of a set of fixed monitoring times. In many situations, it is useful to consider a case-control sampling scheme. Here, …

Current Status Data: Review, Recent Developments And Open Problems, Nicholas P. Jewell, Mark J. Van Der Laan

U.C. Berkeley Division of Biostatistics Working Paper Series

Researchers working with survival data are by now adept at handling issues associated with incomplete data, particular those associated with various forms of censoring. An extreme form of interval censoring, known as current status observation, refers to situations where the only available information on a survival random variable T is whether or not T exceeds a random independent monitoring time C. This article contains a brief review of the extensive literature on the analysis of current status data, discussing the implications of response-based sampling on these methods. The majority of the paper introduces some recent extensions of these ideas to …

Il-10 And Alveolar Bone Loss, Abdulaziz Saud Al-Rasheed

Loma Linda University Electronic Theses, Dissertations & Projects

Interleukin-10 (IL-10) is a cytokine with anti-inflammatory activities. IL-10 knockout (KO) mice exhibit severe intestinal inflammation in the presence of normal gut flora. We hypothesized that IL-10 KO mice would also be susceptible to inflammatory periodontal disease resulting in alveolar bone loss (ABL). The purpose of this study was to compare naturally occurring ABL in IL-10 KO and wild type (WT) mice. Twelve IL-10 KO and 12 WT mice, age-(7 months) and sex-(male) matched, were used. Half of the mice were on 129/SvEv and half on C57BL/6J background. Animal heads were defleshed and treated to remove all organic material. ABL …

Comparative Genomic Hybridization Array Analysis, Annette M. Molinaro, Mark J. Van Der Laan, Dan H. Moore

U.C. Berkeley Division of Biostatistics Working Paper Series

At the present time, there is increasing evidence that cancer may be regulated by the number of copies of genes in tumor cells. Through microarray technology it is now possible to measure the number of copies of thousands of genes and gene segments in samples of chromosomal DNA. Microarray comparative genomic hybridization (array CGH) provides the opportunity to both measure DNA sequence copy number gains and losses and map these aberrations to the genomic sequence. Gains can signify the over-expression of oncogenes, genes which stimulate cell growth and have become hyperactive, while losses can signify under-expression of tumor suppressor genes, …

Prevalence Of Various Upper Extremity Disorders In Patients With Carpal Tunnel Syndrome Versus Patients Without Carpal Tunnel Syndrome, Daniel C. Buda

Loma Linda University Electronic Theses, Dissertations & Projects

Background and Purpose: Increasingly larger numbers of patients present with repetitive strain injuries of the upper extremities, especially carpal tunnel syndrome (CTS). A large number of these patients appear to have more than one upper extremity condition. The purpose of this study was to determine the probability that a patient diagnosed with carpal tunnel syndrome will also be diagnosed with other upper extremity and/or cervical spine disorders.

Subjects: A group of 188 subjects diagnosed with carpal tunnel syndrome and a group of 203 subjects without carpal tunnel syndrome were selected through a chart review of patients at Loma Linda …

Estimating Causal Parameters In Marginal Structural Models With Unmeasured Confounders Using Instrumental Variables, Tanya A. Henneman, Mark Johannes Van Der Laan, Alan E. Hubbard

U.C. Berkeley Division of Biostatistics Working Paper Series

For statisticians analyzing medical data, a significant problem in determining the causal effect of a treatment on a particular outcome of interest, is how to control for unmeasured confounders. Techniques using instrumental variables (IV) have been developed to estimate causal parameters in the presence of unmeasured confounders. In this paper we apply IV methods to both linear and non-linear marginal structural models. We study a specific class of generalized estimating equations that is appropriate to these data, and compare the performance of the resulting estimator to the standard IV method, a two-stage least squares procedure. Our results are applied to …

Peer Nutrition Education: A Model For Nutrition Education Among Spanish-Language Participants Of The Special Supplemental Nutrition Program For Women, Infants And Children (Wic), Maximino Alfredo Mejía

Loma Linda University Electronic Theses, Dissertations & Projects

Despite the steady improvement in the health status of Americans, Hispanics are a minority in the United States with greater prevalence of several infectious and chronic diseases and less health knowledge than the average citizen. Nearly half of the Hispanics living in this country die of preventable nutrition-related conditions, with heart disease and cancer being the leading causes. Since this minority has limited access to health care and preventive services, there is a need for an inexpensive, viable model of health education for this underserved segment of the population in order to lower the excess of preventable diseases. We trained …

The Role Of Diet And Physical Activity For Ovarian Cancer Results From The Adventist Health Study, Fatemeh Kiani

Loma Linda University Electronic Theses, Dissertations & Projects

A few aspects of the epidemiology of ovarian cancer are well understood, such as the inverse relationship with parity and oral contraceptive (OC) use. The role of other factors such as the potential influence of diet or physical activity is far from being established. A few studies, however, have been able to identify dietary risk factors for ovarian cancer. In this dissertation, I have conducted two studies that investigate the relationship between dietary factors and physical activity and the three endpoints: 1) nonfatal ovarian cancer (1976-1982; time to diagnosis), 2) fatal ovarian cancer (1976-1988; time to death), and 3) total …

Anatomy And Three-Dimensional Reconstructions Of The Brain Of A Bottlenose Dolphin (Tursiops Truncatus) From Magnetic Resonance Images, Lori Marino, Keith D. Sudheimer, Timothy L. Murphy, Kristina K. Davis, D. Ann Pabst, William A. Mclellan, James K. Rilling, John I. Johnson

Veterinary Science and Medicine Collection

Cetacean (dolphin, whale, and porpoise) brains are among the least studied mammalian brains because of the formidability of collecting and histologically preparing such relatively rare and large specimens. Magnetic resonance imaging offers a means of observing the internal structure of the brain when traditional histological procedures are not practical. Furthermore, internal structures can be analyzed in their precise anatomic positions, which is difficult to accomplish after the spatial distortions often accompanying histological processing. In this study, images of the brain of an adult bottlenose dolphin, Tursiops truncatus, were scanned in the coronal plane at 148 antero-posterior levels. From these scans …

Optimum Bonding Time Of Four Different Curing Lights, Nathan Don Cotten

Loma Linda University Electronic Theses, Dissertations & Projects

With the development of new high-intensity curing lights, the time required to bond orthodontic brackets is steadily decreasing. The objective of this study was to determine the optimum curing time for bonding orthodontic brackets using four different visible curing lights (Standard Optilux 501, High Intensity Optilux 501 with Turbo Tip, Virtuoso Plasma Arc, and ESPE LED light). This study also tested the new generation of light emitting diode (LED) lights to determine if they can be used for bonding orthodontic brackets. Three hundred freshly extracted bovine teeth were mounted in acrylic resin and divided into 20 groups of 15 teeth …

The Differential Impact Of Sexism In Latino Men And Women’S Psychiatric Symptoms, Astrid Magalij Reina-Patton

Loma Linda University Electronic Theses, Dissertations & Projects

The study assessed the reliability of the Spanish and English versions of the Schedule of Sexist Events General Form (SSE-G). The extent to which Spanish and English-speaking men and women differed in their responses on the SSE-G was investigated, as was the degree to which men and women differed in their report of psychiatric symptoms. Further, the extent to which the SSE-G predicted psychiatric symptomology for Spanish and English-speaking men and women was assessed, as was the extent to which sexism (i.e., gender-specific stress) accounted for additional variance in symptoms, above and beyond that accounted for by acculturation, language, and …

Magnetic Resonance Imaging And Three-Dimensional Reconstructions Of The Brain Of A Fetal Common Dolphin, Delphinus Delphis, Lori Marino, Timothy L. Murphy, Lyad Gozal, John I. Johnson

Veterinary Science and Medicine Collection

To demonstrate the kinds of data that can be obtained non-destructively and non-invasively from preserved museum specimens using modern imaging technology the head region of a whole body fetal specimen of the common dolphin, Delphinus delphis, aged 8–9 months post-conception, was scanned using Magnetic Resonance Imaging (MRI). Series of scans were obtained in coronal, sagittal and horizontal planes. A digital three-dimensional reconstruction of the whole brain was prepared from the coronal series of scans. Sectional areas and three-dimensional volumes were obtained of the cerebral hemispheres and of the brainstemplus-cerebellum. Neuroanatomical features identified in the scans include the major sulci of …

Hand Intensive Leisure Activities And Repetitive Motion Injuries Of The Distal Upper Extremities, Marilyn Colvin Wright

Loma Linda University Electronic Theses, Dissertations & Projects

Background. The work-relatedness of repetitive motion injuries to the distal upper extremities (RMI-DUEs) has been well documented; however, human occupation extends beyond the job to include self-care and leisure activities. The effects of hand intensive leisure activities (HILAs) such as home computer use and needlework on RMI-DUEs have not been explored. These HILAs require hand usage similar to known work-related risk factors. Additionally, sedentary leisure contributes to obesity thereby increasing the disease burden of women. Health beliefs regarding leisure and fitness among women employed in hand intensive sedentary jobs have not been explored.

Purpose. The purpose of this study was …

Probabilities Of Transition Among Health States For Older Adults, Paula Diehr, Donald L. Patrick

UW Biostatistics Working Paper Series

Goal: To estimate the probabilities of transition among self-rated health states for older adults, and examine how they vary by age and sex. Methods: We used self-rated health (Excellent, Very Good, Good, Fair, Poor, Dead) collected in two longitudinal studies of older adults (Mean age 75) to estimate the probability of transition in two years. We used the estimates to project future health for selected cohorts.

Findings: These older adults were most likely to be in the same health state 2 years later, but a substantial proportion changed in both directions. Transition probabilities varied by initial health state, age and …

An Extension Of Euclidean Distance Matrix Analysis Applied To Craniofacial Growth Prediction, Mark K. Batesole

Loma Linda University Electronic Theses, Dissertations & Projects

This study is [sic] introduces a new extension of Euclidean Distance Matrix Analysis (EDMA) as applied to growth prediction analysis. Using EDMA eliminates the presupposition of a set growth pattern, which is introduced by traditional superimposition techniques. When EDMA is extended to analyze prediction methodologies, using a non-age-matched growth sample, some shortcomings become evident. These involve bootstrapping techniques, relative difference in growth, and absence of clinical, real world measure. To overcome these issues, a statistical approach using the Wilcoxen signed rank test, absolute difference in growth, and a new method to evaluate the error in a prediction methodology's landmark identification …

Associations Among Hospital Capacity, Utilization, And Mortality Of Us Medicare Beneficiaries, Controlling For Sociodemographic Factors., E. S. Fisher, J. E. Wennberg, T. A. Stukel, J. S. Skinner, S. M. Sharp

Dartmouth Scholarship

To explore whether geographic variations in Medicare hospital utilization rates are due to differences in local hospital capacity, after controlling for socioeconomic status and disease burden, and to determine whether greater hospital capacity is associated with lower Medicare mortality rates.

Predicting Milk And Soft Drink Consumption Among Female Adolescents Using The Theory Of Planned Behavior, Nada Osman Kassem

Loma Linda University Electronic Theses, Dissertations & Projects

A total of 756 female adolescents, aged 13 to 18 years, from five public high schools in Antelope Valley Union High School District located in North Los Angeles County participated in this study between February 1999 and March 1999. The ethnic composition was 53.3% White/Anglo Americans, 19.3% Hispanics or Latinos and 10.2% Black/African Americans. The constructs of the Theory of Planned Behavior (attitude, subjective norm, and perceived behavioral control and their underlying beliefs) were assessed to determine the predictors of low-fat milk and regular soda consumption. A cross-sectional design with group-administered questionnaires was utilized.

Most participants (89.6%, n = 636) …

Risk Factors Associated With Infant Mortality Among Very Low Birthweight Infants Of Teenage Mothers In San Bernardino County, C. Letitia Henry

Loma Linda University Electronic Theses, Dissertations & Projects

Background. Typically, infant mortality decreases as maternal age increases in teenagers. In contrast to these national data, San Bernardino County (SBC) experienced a different phenomenon in 1989-1994 among very low birthweight (VLBW) infants. The infant mortality rate (IMR) of VLBW infants born to mothers under 17 years old (283 per 1000 live births) was significantly lower than the IMR of VLBW infants born to mothers between the ages of 17-19 years old (430 per 1000 live births) (p = .02).

Purpose. The purpose of the study was to explain the discrepancy between IMRs of VLBW infants of younger teenage mothers …

The Association Of Fluid Intake With Total Natural-Cause Mortality, Coronary Heart Disease And Fatal Stroke, Jacqueline Chung Lun Chan

Loma Linda University Electronic Theses, Dissertations & Projects

Hypohydration may be more widespread than realized since it does not always arouse a sense of thirst. When thirst is felt, it is often ignored, or satisfied before euhydration is achieved. There is growing evidence indicating that hypohydration contributes to acute and chronic illnesses, and to rheological factors associated with coronary heart disease (CHD) and stroke. Therefore the relationship of fluid intake with risk of total natural-cause mortality, CHD and stroke death was examined using data on 34,192 white, non-Hispanic participants in the Adventist Health Study.

Among the 27,342 reporting no CHD, stroke or diabetes at baseline, during six years …

Body Weight And Mortality Among Adults Who Never Smoked, Pramil N. Singh

Loma Linda University Electronic Theses, Dissertations & Projects

Most prospective studies identify an increased mortality risk for adults of high body mass index (> 27 kg/m²) that is commonly attributed to the effects of excess body fat, and also identify an increased mortality risk for adults of low body mass index (< 21 kg/m²), an association that, if causal among healthy adults, is without adequate pathophysiologic support.

In this dissertation, I have conducted three studies that continue the investigation of adiposity in relation to mortality among never-smoking adults of the California Seventh-day Adventist population. Among never-smoking adults of the Adventist Mortality Study (1960-1985), the relation between …